Repeat string to certain length

Question

What is an efficient way to repeat a string to a certain length  Eg  repeat  abc   7  - gt   abcabca   Here is my current code   def repeat string  length       cur  old   1  string     while len string   lt  length          string    old cur-1          cur    cur 1  len old      return string   Is there a better  more pythonic  way to do this  Maybe using list comprehension

User · Accepted Answer

def repeat to length string to expand  length      return  string to expand     length len string to expand   1    length    For python3   def repeat to length string to expand  length       return  string to expand    int length len string to expand   1    length

User · Answer

Another FP aproach   def repeat string string to repeat  repetitions       return    join   string to repeat for n in range repetitions

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This is one way to do it using a list comprehension  though it s increasingly wasteful as the length of the rpt string increases   def repeat rpt  length       return    join  rpt for x in range 0   len rpt    length      length

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def rep s  m       a  b   divmod m  len s       return s   a   s  b

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from itertools import cycle  islice def srepeat string  n      return    join islice cycle string   n

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Not that there haven t been enough answers to this question  but there is a repeat function  just need to make a list of and then join the output   from itertools import repeat  def rep s n        join list repeat s n

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i use this    def extend string s  l       return  s l   l

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How about string    length   len string     string 0  length   len string

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Jason Scheirer s answer is correct but could use some more exposition   First off  to repeat a string an integer number of times  you can use overloaded multiplication    gt  gt  gt   abc    7  abcabcabcabcabcabcabc    So  to repeat a string until it s at least as long as the length you want  you calculate the appropriate number of repeats and put it on the right-hand side of that multiplication operator   def repeat to at least length s  wanted       return s    wanted  len s    1    gt  gt  gt  repeat to at least length  abc   7   abcabcabc    Then  you can trim it to the exact length you want with an array slice   def repeat to length s  wanted       return  s    wanted  len s    1    wanted    gt  gt  gt  repeat to length  abc   7   abcabca    Alternatively  as suggested in pillmod s answer that probably nobody scrolls down far enough to notice anymore  you can use divmod to compute the number of full repetitions needed  and the number of extra characters  all at once   def pillmod repeat to length s  wanted       a  b   divmod wanted  len s       return s   a   s  b    Which is better  Let s benchmark it    gt  gt  gt  import timeit  gt  gt  gt  timeit repeat  scheirer repeat to length  abcdefg   129    globals globals     0 3964178159367293  0 32557755894958973  0 32851039397064596   gt  gt  gt  timeit repeat  pillmod repeat to length  abcdefg   129    globals globals     0 5276265419088304  0 46511475392617285  0 46291469305288047    So  pillmod s version is something like 40  slower  which is too bad  since personally I think it s much more readable   There are several possible reasons for this  starting with its compiling to about 40  more bytecode instructions   Note  these examples use the new-ish    operator for truncating integer division   This is often called a Python 3 feature  but according to PEP 238  it was introduced all the way back in Python 2 2   You only have to use it in Python 3  or in modules that have from   future   import division  but you can use it regardless

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This is pretty pythonic   newstring    abc  5 print newstring 0 6

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Yay recursion   def trunc s l       if l  gt  0          return s  l    trunc s  l - len s       return      Won t scale forever  but it s fine for smaller strings  And it s pretty   I admit I just read the Little Schemer and I like recursion right now

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def extended string  word  length         extra long word   word    length  len word    1      required string   extra long word  length      return required string  print extended string  abc   7

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Perhaps not the most efficient solution  but certainly short  amp  simple   def repstr string  length       return  string   length  0 length   repstr  foobar   14    Gives  foobarfoobarfo    One thing about this version is that if length  lt  len string  then the output string will be truncated   For example   repstr  foobar   3    Gives  foo    Edit  actually to my surprise  this is faster than the currently accepted solution  the  repeat to length  function   at least on short strings   from timeit import Timer t1   Timer  repstr  foofoo   30     from   main   import repstr   t2   Timer  repeat to length  foofoo   30     from   main   import repeat to length   t1 timeit      gives  0 35 secs t2 timeit      gives  0 43 secs   Presumably if the string was long  or length was very high  that is  if the wastefulness of the string   length part was high  then it would perform poorly   And in fact we can modify the above to verify this   from timeit import Timer t1   Timer  repstr  foofoo    10  3000     from   main   import repstr   t2   Timer  repeat to length  foofoo    10  3000     from   main   import repeat to length   t1 timeit      gives  18 85 secs t2 timeit      gives  1 13 secs

[string] Repeat string to certain length

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